Hydraulic drive fuel system



April 7, 1942. D. sAMlRAN Erm.

HYDRAULIC DRIVE FUEL SYSTEM Filed Marnh 4, 1941 /N vA-N was 0,4 a//a LvM/en/v Patented Apr. 7, "1942 -nrnaAUmc DRIVE FUEL SYSTEM David Samiran and Roy B. Poole, Dayton, Ohio Application Maren 4, 1941, semi No. 381,690

(Granted under the act of March l3, 1883, as mended April 30, 192s: 370 '0- G. 757) 6 Claims.

The invention described herein may be manufactured and used by or for the Goverment for governmental purposes. without the payment to us of any royalty thereon.

This invention relates to a fuel system for an internal combustion engine employing a variable speed hydraulic drive for the fuel pump and particularly weli adapted for use in aircraft intended for use at high altitudes.

Many dimculties due to vapor locking in the fuel systems of aircraft intended to operate at high altitudes have occurred and these dimculties are traceable to two sources. The first'type arises by employing a fuel pump mounted on and directly driven by the engine, with themean fuel level in the tanks such that the pump is required to exert a suction lift whiclr at high altitudes exceeds the vapor pressurev of the fuel and the line ilow resistance at high altitudes, causing the fuel to vaporize and unprime the pump. A second type of failure arises by employing a relief valve to maintain a constant fuel pressure in the pump delivery conduit which allows the fuel to ing a pressure responsive control, responsive to variation in fuel pressure in the delivery conduit preferably at the point of delivery, for controlling the speed of the driven endof the hydraulic transmission and fuel pump, the fuel pressure may be'maintained constant irrespective of the' demand for fuel, thus eliminating the relief valve and by-pass heretofore associated with the fuel pump. Such a type of fuel system is disclosed in United States Patent No. 2,229,132 granted to David Samiran and in our copending application Serial No. 380,396 filed February 24, 1941, for' Aircraft fuel systems. The patented fuel sysy tem and at least one of the fuel systems illus-A trated in\our above noted copending application requires the use of an external y engine driven pump to serve as the pressure generator or driving end of the variable speed hydraulic transmission used to drive the fuel pump. The use of a separate engine driven pump for the driving end .of the hydraulic 'ton necessarily in creases the weight and cost of the' fuel system as welll as complicates the already overburdened aecessory driving system of the present type'aircraft engines. The present invention eliminates the necessity of employing a separate engine driven pressure generator or pump for the driving element of the hydraulic transmission by employing the pressure oiling system of the engine as a a source of motive fluid for the hydraulic transl mission. The hydraulic transmission fluid circuit conduit substantially constant.

means responsive to the variation in the fuel pressure in the fuel'pump delivery conduit from a` predetermined value is employed to control the pressure drop across the hydraulic motor to thereby vary its speed to maintain the fuel pump output pressure at a selected point in the delivery The invention also contemplates the use of al modifier in con- Junction with the pressure responsive control means, whereby the modiiier is responsive to a pressure such as the engine intake manifold pressu1e, so that the net control eifect is dependent on the existing. pressure differential between the manifold pressure'and the fuel pressure in the delivery conduit.

The invention also provides a modified con# struction in which the hydraulic vmotor is of the -variable capacity type and having' a means to vary the capacity to thereby alter the pressure drop across the motor to vary its speed i. e., with the constant pressure source of motive fluid the motor speed will increase with decrease of capacity and vice versa. The capacity control meansv is directly actuated by a pressure responsive control means in thesame manner as in the previousl'y described fuel pump drive.

The principal objectof the` invention is the provision of a fuel system for an internal combustion engine having a pressure oiling system, in-

cluding a source of fuel supply, a delivery conduit, a fuel pumpfor pumping. fuel from said source to said conduit under pressurefor consumption by the engine, a hydraulic motor for driving the pump, a fluid circuit connecting the hydraulic motor and the engine oiling system and control means responsive to the variation in the delivery pressure of fuel'insaid delivery conduit from a predetermined pressure for controlling the flow of oil through said uid circuit to thereby vary the speed of said hydraulic motor and the output of said fuel pump.

from, of control means responsive to the varia-.-

tions in pressure of the fuel at the point of delivery from a predetermined value for controlling the pressure drop across said hydraulic motor and thereby controlling its'speed and the output of said fuel pump.

A further object of the invention is the provision in a fuel system of the character described having a fuel pump driven by a hydraulic motor connected to the engine oiling system through a fluid circuit, of pressure responsive means for controlling the flow of oil through said circuit in accordance with the differential between the pressure of the fuel at the point of delivery and a reference fluid pressure indicative of engine load.

Other objects of the invention not specifically enumerated'above will appear by reference to the detailed description in the specification and to the appended drawing in which:

Fig. 1 is a diagrammatic illustration of the principal elements of a fuel system in accordance with the invention; and

Fig. 2 is a sectional view taken online 2 2. of

Fig. 1, illustrating details of a portion of the enfrom the conventional oat chamber 5, the com-- bustible mixture being supplied to the engine intake manifold 1. The float chamber is provided with fuel by means of a delivery conduit 6, connected to the, delivery side of a positive displacement fuel pump 3, which has its inlet side connected by means of conduit 9 to a source of fuel supplyl III, which may comprise one or more xfuel tanks delivering fuel to a collector not shown. The positive .displacement fuel pump 3 is adapted todae driven at varying speeds by means ofa hydraulic motor ,I2 provided with a tachometer take on drive I3, adapted to drive a tachometer not shown, to indicate the rate of fuel consmnption in terms of the pump velocity. The hydraulic motor I2 is supplied with motive fluid from a fluid circuit connected to the oiling system of the .engine I, in a maner now to be de- The engine I is provided with the conventional drilled crank shaft Il rotatably mounted in bearingsll, which are supplied with lubricating oil under pressure from conduits I1 connected in parallel to a conduit I3, which in turn is connected to the'output or high pressure side of a conventional oil pump 2l. The oil pump 2l is adapted to be driven by 'means of a shaft 2l and gears 22v and 23 from an extension shaft 24, iii-turn driven from the engine crank shaft by means of the bevel gears 2l and 23. The oil pump 2l is provided with a pressure relief valve 21, which is adapted to by-pass oil from the pressure side of the pump by means of a conduit 23 to the engine oil tank 30, to thereby maintain the pressure at the delivery side of the pump substantially constant (see also Fig. 2). The pump 20 receives its oil supply by means of the conduit 29, connected to the sump'of the oil tank 3U. Oil under pressure from the delivery side of the pump 20 is also delivered to a pressure conduit 3| (see also Fig. 2) which serves in commotion with the conduit 3l to deliver oil under pressure to the hydraulic motor I2, the oil discharged by the motor being /returned to the engine oiling system through the conduit 32 connected to the engine oil tank 3II. The speed of rotation of the hydraulic motor I2 is controlled by regulating the flow of oil through the pressure conduits 3| and 3l' by means of a pressure responsive control device generally indicated by the reference numeral 35. The pressure responsive control device 35 comprises a sealed housing 36 having an extension housing or valve chamber 31 secured thereto, the housing 36 inclosing a flexible metal .bellows 38, which is secured at one end to an end wall of the housing 36 and having its other end connected to a control rod 39 projecting throughthe end wall of the housing 3l into the valve casing 31 and urged in one direction by means of a compression spring 40 concentric with the control rod 39, the loading of which is varied by adJustment of the threaded abutment 4I. The valve casing 31 is provided with a central wall 42 dividing thecasng into chambers 43 and 44, which are in communicationby means of a valve port 45 formed in the wall 42 and the communication between the chambers being controlled by means of a throttle valve 46 concentrically mounted on the control rod 39. The chamber 43 is adapted to receive oil under pressure from the conduit 3| and oil discharged from the chamber 43 to the chamber through valve port 45 is conducted to the hydraulic motor I2 through the conduit 3I' connected thereto. The space inclosed between the outer portion of the bellows 38 and the interior of the housing 33 is in communication with the pressure in the fuel delivery conduit 6 at the point of delivery to the float chamber l, by means of the branch conduit 6', and the interior of the bellows 3l is connected by means of a conduit lll to the intake manifold 1 of the engine I. It will be seen that the force exerted upon the control rod 39 in opposition to the loading of the spring" will be equal to the force exerted on the bellows bythe differential in pressure betweenthe fuel pressure acting on the outside of the bellows and the intake manifold pressure acting on the inside of the bellows,

the resultant control force tending to move the throttle control valve 40 relative to the port 45, to thereby control the flow of oil to the hydraulic motor I2.

Operation The operation of the device of Figure 1 is as follows:

The engine is started by means of fuel pumped g to the carburetor by means of a conventional hand pump, not shown and after the engine starts 2,278,493 downward to move the throttle valve 4i in the closingdirection to thereby governthe speed of l the hydraulicmotor I2 to maintain the quantity of fuel pumped by the fuel pump l to the carburetor 2, in exactly the right amount to supply the engine fuel demand and still maintain the fuel pressure at the point of delivery to the carburetor constant'atV a predetermined value, for example, ilve pounds per-sq. in. Where the engine is employed to vpropel an aircraft, the engine load and hence the fuel demand will vary von the differential in pressure between the engine manifold pressure (indicative of engine load) and the fuel 'pressure at the point of dev livery, rather than 'by the relation oi' the fuel pressure to the pressure of the outside atmo sphere, so that although the aircraft is ascending,

the changes in atmospheric pressure will not directly effect the response of .the control v'device and the control of the fuel System will be in response to changes in the engine load, as

well as variation in fuel pressure from the predetermined pressure set by the adjustment of the loading of the spring ll. The provision of the means for subjecting the interior of the bellows Il to the engine manifold pressure serves as a modifier for the action of the bellows' under the influence of the fuel pressure ,admitted the housing Il.

It will be noted that by employing the engine oiling system .as a source of motive iiuid for the hydraulic transmission for driving the fuel pump l, it is not necessary to employ a separate engine driven pressure generator in the hydraulic circuit,

thus materially reducing the weight and complication of the fuel system and further. the pressure relief valve of the engine oiling pump prevents with the displacement of the lever. The lever 65' is pivotally connected directly to the control rod 3l of the pressure responsive control device 35 (Figa l) so that the control device directly changes the capacity of the motor I2', in a manner such that the speed of the motor. is increased by reducing the motor capacity upon a decrease in fuel pressure and that the motor capacityl is increased and the motor speed reduced upon an increase of fuel pressure above the predetermined value. The modified speed control illustrated in Figure3 may be bodily inserted inthe device of Figure l to replace the hydraulic motor I2 and its function. 'Ihe variable capacity hydraulic motor I2 having its inlet connecteddirectly to the conduit 2 I to receive oil under pressure from the engine oil'ing system and having its outlet connected directly to the' discharge conduit 32. the connections of the fuel pump 8 to the conduits l and 9, and the connection of the pressure responsive device to the conduits l' and it respectively, are made in exactly the same manner as in the fuel system of Figure 1, the complete.

fuel system not being illustrated because the insertion of the modified drive of Figure 3 to serve its proper function in the fuel system of Figure l, is believed to be sumciently clear so as not toreq'uire separate illustration.-

While the preferred forms of our invention have been illustrated and described, it will be any. excessive rise, in pressure in the hydraulic drive and further'serves as a torque limiting de-l vice for the hydraulic motor I2, since the pressure in the hydraulic driving system can never exceed the pressure existing at the output side of the lubricating pump 2l. While the device of Figure 1 has been illustrated as incorporating a throttle valve in the pressure side of the hydraulic circuit for controlling the speed of the motor I2. it is obvious'that the motor speed could 'be controlled in exactly the ysame manner by trated in Figure 3, the pressure drop across the motor I2' is controlled by varving the capacity of the hydraulic motor driving the pump l, in placev of the use of a throttle valve. -As seen in Figure 3, the variable capacity hydraulic motor I2', which may beany suitable type such as a vane type motor having a stator shiftable eccentrically with respect to the vaned'rotor is provided with a I control rod 6I, projecting 'from the motor housing and being provided with rack teeth l2, which mesh with the teeth oi a pinion gear l2 mounted on a shaft Il, which is rotated by means of lever totherebycauseaxialshiftingofthecapacity modifications and changes may be made therein falling within the scope of the invention as de4 ilned by the appended claims.

We claim:

. said motor including an oil pressure conduit and an oil return conduit, a throttle valve in said pressure conduit Afor controlling the admission 'of motive fluid to said motor, and pressure responsive means responsive to variation in fuel pressure in said fuel`conduit from a predetermined value for controlling sfaid valve means to thereby control the speed of lrvdraulic motor and said fuel pump to maintain the fuel preure in said fuel conduit substantially constant.

2. A fuel system for an internal combustion engine having a relief valve controlled pressure oiling system comprising, a source of fuel supply, a delivery conduit, a constant displacement pump throttle valve in said circuit for controlling the flow of oil through said motor from said oiling system and means -responsive to the variationin the pressure of fuel in said delivery conduit for actuating said control valve.

3. The structure as claimed in claim 2, in which the pressure responsive means includes a modifier responsive to variation in engine intake manifold pressure, whereby said throttle valve is actuated in response to the differential between said last named pressure and the fuel pressurein the control rod ll in either direction, in accordance delivery conduit.

1. A fuel system for an internal combustion.

4. In a fuel system for an internal combustion engine having a relief valve controlled pressure oiling system and an intake manifold, a source of fuel supply, a delivery conduit for conducting y fuel to the engine for consumption thereby, a fuel pump connected to said fuel supply and to said delivery conduit, a hydraulic motor connected to said pump'to `drive the same, a fluid circuit including a conduit connected to the pressure side of the engine oiling system and a discharge conduit connected to the return side of the oiling system, said hydraulic motor being serially connected to said conduits, and pressure responsive control means for controlling the drop in pressure between said conduits across said hydraulic motor to thereby vary the motor speed, said pressure responsive means being responsive to the variation in fuel pressure in said delivery conduit at the point of delivery.

5. In a fuel system for an internal combustion engine having a relief valve controlled pressure oiling system, a fuel supply, a conduit for conducting fuel under pressure to the ensine for consumption thereby, a fuel pump connected to said supply and to said conduit, a variable capacity hydraulic motor for driving said pump. a fluid circuit connecting said motor and the engine oiling system to receive motive duid under pressure therefrom, and pressure rponsive control means responsive to variations in the fuel pressure at the point of delivery for varying the capacity of the hydraulic motor to thereby vary its speed and the delivery of the fuel pump.

6. The structure as claimed in claim 5, in which said pressure responsive control means includes a modii'ier for modifying the control effect thereof in response to the instant pressure in the engine intake manifold.

DAVID SAMJRAN. ROY B. POOLE. 

